Several common models are used in designing backup plans. Each has its own advantages and
disadvantages. Numerous methods have been developed to deal with backup archival; most of
them are evolutions of the three models discussed here:
Grandfather, Father, Son Method The Grandfather, Father, Son method is based on the phi-
losophy that a full backup should occur at regular intervals, such as monthly or weekly. This
method assumes that the most recent backup after the full backup is the son. As newer backups
are made, the son becomes the father, and the father, in turn, becomes the grandfather. At the
end of each month, a full backup is performed on all systems. This backup is stored in an offsite
facility for a period of one year. Each monthly backup replaces the monthly backup from the
previous year. Weekly or daily incremental backups are performed and stored until the next full
backup occurs. This full backup is then stored offsite http://h2obeta.law.harvard.edu/299191 , and the weekly or daily backup tapes are
reused (the January 1 incremental backup is used on February 1, and so on).
This method ensures that in the event of a loss, the full backup from the end of the last month
and the daily backups can be used to restore information to the last day. Figure 9.4 illustrates
this concept: The annual backup is referred to as the grandfather, the monthly backup is the
father, and the weekly backup is the son. The last backup of the month becomes the archived
backup for that month. The last backup of the year becomes the annual backup for the year.
Annual backups are usually archived; this allows an organization to have backups available for
several years and minimizes the likelihood of data loss. It’s a common practice for an organi-
zation to keep a minimum of seven years in archives.
The last full backup of the year is permanently retained. This ensures that previous years’ infor-
mation can be recovered if it’s needed for some reason.